Wind turbine generator system, wind turbine blade, and reinforcing method for wind turbine blade

ABSTRACT

A wind turbine blade is reinforced while suppressing possible stress concentration resulting from a load imposed on a blade root portion of the wind turbine blade in a flap direction. The wind turbine blade includes a blade main body extending from the blade root portion toward a blade tip portion and an FRP reinforcing layer formed so as to cover at least a part of the outer surface of the blade root portion of the blade main body. The FRP reinforcing layer includes a plurality of laminated fiber layers and a resin with which the plurality of fiber layers is impregnated. The FRP reinforcing layer is formed such that, in a cross section along a longitudinal direction of the blade main body, both ends of the plurality of laminated fiber layers in the longitudinal direction are tapered.

RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.15/705,245 filed Sep. 14, 2017, and claims priority from JapaneseApplication Number 2017-021890, filed Feb. 9, 2017, the disclosure ofwhich is hereby incorporated by reference herein in its entirety.

TECHNICAL FIELD

The disclosure relates to a wind turbine generator system, a windturbine blade, and a reinforcing method for a wind turbine blade.

BACKGROUND

As is known, loads in various directions act on wind turbine blades usedin a wind turbine generator system (hereinafter referred to as awindmill). In particular, at the time of a strong wind, a heavy loadacts on a blade root portion of each wind turbine blade in a flapdirection. On the other hand, windmills are generally required to have aprolonged service life. Thus, there have been growing needs to providewind turbine blades with additional reinforcements as needed in order todeal with possible degradation of or possible fatigue damage to the windturbine blades resulting from long-term use thereof.

In regard to reinforcement of the wind turbine blades, Patent Document 1discloses a technique for adding reinforcing ribs to an innercircumference or an outer circumference of the blade root portion of thewind turbine blade along a circumferential direction of the blade rootportion. Specifically, in the technique disclosed in Patent Document 1,circular-arc-shaped reinforcing ribs are additionally provided around apart or all of the inner or outer circumference of the blade rootportion. Both ends of the circular arc of each of the ribs are taperedalong the circumferential direction of the blade root portion.

CITATION LIST Patent Literature

-   Patent Document 1: US 2015-093250 A1

SUMMARY

However, although Patent Document 1 discloses the reinforcing techniquefor preventing the blade root portion, which is cross-sectionally shapedgenerally like a cylinder as viewed in an axial direction along alongitudinal direction of the wind turbine blade, from being deflectedby a load and deformed into an elliptic shape, this document disclosesno measures against the load acting on the blade root portion in theflap direction. Thus, in Patent Document 1, the thickness of the windturbine blade including the rib varies sharply at a boundary between apart of the blade root portion to which the rib has been added and apart thereof to which no rib has been added, disadvantageously resultingin stress concentration when a load is imposed.

An object of at least several embodiments of the present invention is toreinforce the wind turbine blades while suppressing possible stressconcentration resulting from a load imposed on the blade root portion ofeach wind turbine blade in the flap direction.

(1) A wind turbine blade according to at least one embodiment includes:

a blade main body extending from a blade root portion toward a blade tipportion; and

an FRP reinforcing layer formed so as to cover at least a part of anouter surface of the blade root portion of the blade main body, and

the FRP reinforcing layer includes:

a plurality of laminated fiber layers; and

a resin with which the plurality of fiber layers is impregnated, and

the FRP reinforcing layer is formed such that, in a cross section alonga longitudinal direction of the blade main body, both ends of theplurality of laminated fiber layers in the longitudinal directionthereof are tapered.

According to the configuration in (1), at least a part of the outersurface of the blade root portion of the blade main body may be covered,for reinforcement, with the FRP reinforcing layer including theplurality of fiber layers impregnated with the resin. In a cross sectionalong the longitudinal direction of the blade main body, both ends ofthe FRP reinforcing layer in the longitudinal direction of the pluralityof laminated fiber layers are tapered. This inhibits a sharp variationin the thickness of the root portion of the wind turbine blade includingthe FRP reinforcing layer in the longitudinal direction of the bladeroot portion. Therefore, the configuration in (1) allows the windturbine blade to be reinforced while appropriately suppressing possiblestress concentration resulting from a load imposed on the blade rootportion of the wind turbine blade in the flap direction.

(2) In several embodiments, in the configuration described in (1),

a first tapered shape of a blade tip-side end of both the ends of theplurality of laminated fiber layers is gentler than a second taperedshape of a blade root-side end of both the ends of the plurality oflaminated fiber layers.

In the configuration in (2), both ends of the plurality of laminatedfiber layers may be formed such that the first tapered shape of theblade tip-side end, which has a spare installation area, has asufficiently gentler inclination than the second tapered shape of theblade root-side end. Therefore, the thickness of the blade root portionmay vary sufficiently gradually in the longitudinal direction, allowingthe wind turbine blade to be reinforced while suitably suppressingpossible stress concentration resulting from a load in the flapdirection.

(3) In several embodiments, in the wind turbine blade described in (1)or (2),

the first tapered shape of the blade tip-side end of both the ends ofthe plurality of laminated fiber layers has an inclined surface with agradient of 5% or less with respect to the longitudinal direction.

In the configuration in (3), the inclined surface of the blade tip-sideend of the fiber layers may have a sufficiently gentle gradient of 5% orless with respect to the longitudinal direction of the wind turbineblade. Consequently, the thickness of the blade root portion may varysufficiently gradually in the longitudinal direction, allowing the windturbine blade to be reinforced while appropriately suppressing possiblestress concentration resulting from a load in the flap direction.

(4) In several embodiments, in the wind turbine blade described in anyone of (1) to (3),

the FRP reinforcing layer is formed such that, in a cross section of theblade root portion, both ends of the plurality of laminated fiber layersin a circumferential direction of the blade root portion are tapered.

In the configuration in (4), both ends of the FRP reinforcing layer inthe circumferential direction of the blade root portion arecross-sectionally tapered. Thus, the thickness of the blade root portionmay vary sufficiently gradually in the circumferential direction tosuppress possible stress concentration, while allowing the wind turbineblade to be reinforced.

(5) In several embodiments, in the wind turbine blade described in anyone of (1) to (4),

the FRP reinforcing layer includes an intermediate layer positionedbetween the outer surface of the blade root portion and the plurality offiber layers and formed of a multidirectional fiber layer.

In the configuration in (5), the intermediate layer formed of themultidirectional fiber layer is arranged between the outer surface ofthe blade root portion and the plurality of fiber layers, allowing thefiber layers to be more appropriately bonded to the outer surface of thewind turbine blade. The multidirectional fiber layer refers to a layerin which fibers are arranged in a plurality of directions unlike aunidirectional fiber layer in which fibers are arranged in a singledirection.

(6) In several embodiments, in the wind turbine blade described in (5),

the intermediate layer is a DBM or a chopped strand mat.

In the configuration in (6), the DBM or the chopped strand mat easilyallows the fiber layers to be more appropriately bonded to the outersurface of the wind turbine blade.

(7) In several embodiments, in the wind turbine blade described in anyone of (1) to (6),

the number of the laminated fiber layers is 10 or more and 100 or less.

In the configuration in (7), the wind turbine blade may be reinforced byforming the fiber layers to a needed thickness according to thedistribution of stress near the blade root portion of the wind turbineblade.

(8) In several embodiments, in the wind turbine blade described in anyone of (1) to (7),

the resin is a polyester resin or an epoxy resin.

In the configuration in (8), the FRP reinforcing layer may be formed byimpregnating the fiber layers with a thermoplastic resin such as thepolyester resin or the epoxy resin, which is then cured.

For example, if the fiber layers are impregnated with the polyesterresin, which is then cured, then the resin is cured by self-heating,eliminating the need for an external heating operation to allow the FRPreinforcing layer to be easily and inexpensively formed. If the fiberlayers are impregnated with the epoxy resin, which is then cured, an FRPreinforcing layer may be formed which can be appropriately bonded to theouter surface of the blade root portion.

(9) In several embodiments, in the wind turbine blade described in anyone of (1) to (8),

the blade main body includes:

a suction-side half-section and

a pressure-side half-section that is joined to the suction-sidehalf-section, and

the FRP reinforcing layer is formed, in the circumferential direction ofthe blade root portion, within an angular range of θ₀−50 degrees≤θ≤₀+50degrees when an angular position of a center of a circular arc definedin a cross section of the blade root portion by at least one of thesuction-side half-section or the pressure-side half-section is denotedby 0o.

The configuration in (9) allows appropriate reinforcement of a part ofthe blade root portion on which a heavy load is imposed in the flapdirection by bending stress.

(10) In several embodiments, in the wind turbine blade described in anyone of (1) to (9),

the blade main body has in the blade root portion a bolt hole throughwhich the wind turbine blade is attached to a hub, and

the FRP reinforcing layer is provided further toward a blade tip sidethan an extension range of the bolt hole in the longitudinal direction.

In the configuration in (10), the FRP reinforcing layer is providedfurther toward the blade tip side than the extension range of the bolthole through which the wind turbine blade is attached to the hub. Inother words, the FRP reinforcing layer is inhibited from closing thebolt hole through which the wind turbine blade is attached to the hub.Therefore, the wind turbine blade may be reinforced without hampering afunction to attach the hub to the wind turbine blade via the bolt holeor an operation of performing such attachment.

(11) A wind turbine generator system according to at least severalembodiments includes the wind turbine blade described in any one of (1)to (10).

The configuration in (11) can provide a wind turbine generator systemwith the wind turbine blade including the FRP reinforcing layer inwhich, in a cross section along the longitudinal direction of the blademain body, both ends of the FRP reinforcing layer in the longitudinaldirection of the plurality of laminated fiber layers are tapered,allowing the wind turbine blade to be appropriately reinforced whilesuppressing possible stress concentration resulting from a load imposedon the blade root portion of the wind turbine blade in the flapdirection.

(12) A reinforcing method for a wind turbine blade according to at leastseveral embodiments includes:

laminating fiber layers on an outer surface of a blade root portion of awind turbine blade so as to cover at least a part of the outer surface;and

impregnating the laminated fiber layers with a resin and curing the sameto form an FRP reinforcing layer on the outer surface of the blade rootportion, and

the fiber layers are laminated such that, in a cross section along alongitudinal direction of the wind turbine blade, both ends of theplurality of laminated fiber layers in the longitudinal direction aretapered.

In the method in (12), as described in (1), in a cross section along thelongitudinal direction of the blade main body, both ends of the FRPreinforcing layer in the longitudinal direction of the plurality oflaminated fiber layers are tapered, thus inhibiting a sharp variation inthe thickness of the root portion of the wind turbine blade includingthe FRP reinforcing layer in the longitudinal direction of the bladeroot portion. Therefore, the method allows the wind turbine blade to bereinforced while appropriately suppressing possible stress concentrationresulting from a load imposed on the blade root portion of the windturbine blade in the flap direction.

(13) In several embodiments, in the method described in (12),

a first tapered shape of a blade tip-side end of both the ends of theplurality of laminated fiber layers is gentler than a second taperedshape of a blade root-side end of both the ends of the plurality oflaminated fiber layers.

In the method in (13), as described in (2), both ends of the pluralityof laminated fiber layers may be formed such that the first taperedshape of the blade tip-side end, which has a spare installation area,has a sufficiently gentler inclination than the second tapered shape ofthe blade root-side end. Therefore, the thickness of the blade rootportion may vary sufficiently gradually in the longitudinal direction,allowing the wind turbine blade to be reinforced while suitablysuppressing possible stress concentration resulting from a load in theflap direction.

(14) In several embodiments, the method described in (12) or (13)further includes:

roughening at least a configuration area of the outer surface of theblade root portion where the FRP reinforcing layer is to be configured;and forming an intermediate layer in the roughened configuration area ofthe outer surface of the blade root portion, wherein

the fiber layers are laminated on the intermediate layer.

The method in (14) may involve, instead of laminating the fiber layersdirectly on the outer surface of the blade root portion, roughening atleast the configuration area of the outer surface of the blade rootportion where the FRP reinforcing layer is to be configured, forming theintermediate layer in the roughened configuration area, and laminatingthe fiber layers on the intermediate layer. Therefore, by using, as theintermediate layer, for example, a material that can be appropriatelybonded to the outer surface of the wind turbine blade and to the fiberlayers, the fiber layers may be more appropriately bonded to the outersurface of the wind turbine blade. Consequently, the FRP reinforcinglayer may be formed more integrally with the wind turbine blade,allowing the wind turbine blade to be more firmly reinforced.

(15) In several embodiments, in the method described in any one of (12)to (14),

the step of forming of the FRP reinforcing layer includes:

covering the laminated fiber layers with a bag;

decompressing a space enclosed by the outer surface of the blade rootportion and the bag; and

injecting a resin into the space to impregnate the fiber layers with theresin.

In the method in (15), the fiber layers laminated on the outer surfaceof the blade root portion are covered with the bag, the space enclosedby the outer surface of the blade root portion and the bag isdecompressed, and the resin is injected into the decompressed space.Therefore, the resin may be infiltrated throughout the fiber layers,providing an FRP reinforcing layer having few voids and a high strength.

At least one embodiment of the present invention allows the wind turbineblade to be reinforced while suppressing possible stress concentrationresulting from a load imposed on the blade root portion of the windturbine blade in the flap direction.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram depicting a wind turbine generator systemaccording to an embodiment;

FIG. 2 is a perspective view depicting the whole wind turbine bladeaccording to an embodiment;

FIG. 3 is a perspective view depicting a reinforced portion (FRPreinforcing layer) of the wind turbine blade according to an embodiment;

FIG. 4 is a diagram depicting the reinforced portion of the wind turbineblade according to an embodiment and illustrating the shape of both endsof the FRP reinforcing layer and a configuration area of the FRPreinforcing layer in a circumferential direction of a blade rootportion;

FIG. 5 is a schematic diagram taken along arrow V-V in FIG. 2 andillustrating the shape of the wind turbine blade;

FIG. 6 is a diagram depicting the reinforced portion of the wind turbineblade according to an embodiment and illustrating the shape of both endsof the reinforced portion in a longitudinal direction of the windturbine blade;

FIG. 7 is a diagram depicting a configuration of the FRP reinforcinglayer in an embodiment;

FIG. 8 is a flowchart illustrating a reinforcing method for a windturbine blade according to an embodiment;

FIG. 9 is a flowchart illustrating a reinforcing method for a windturbine blade according to an embodiment;

FIG. 10 is a flowchart illustrating a reinforcing method for a windturbine blade according to an embodiment;

FIG. 11A is a schematic diagram illustrating a step of roughening theconfiguration area of a blade surface, in the reinforcing method for thewind turbine blade according to an embodiment;

FIG. 11B is a schematic diagram illustrating a step of forming anintermediate layer in the roughened configuration are, in thereinforcing method for the wind turbine blade according to anembodiment;

FIG. 11C is a schematic diagram illustrating a step of forming fiberlayers on the intermediate layer, in the reinforcing method for the windturbine blade according to an embodiment;

FIG. 11D is a schematic diagram illustrating a step of covering thelaminated fiber layers with a bag, in the reinforcing method for thewind turbine blade according to an embodiment;

FIG. 11E is a schematic diagram illustrating a step of decompressing aspace enclosed by an outer surface of the blade root portion and thebag, in the reinforcing method for the wind turbine blade according toan embodiment;

FIG. 11F is a schematic diagram illustrating a step of impregnating thefibers layers with a resin, in the reinforcing method for the windturbine blade according to an embodiment; and

FIG. 11G is a schematic diagram illustrating the FRP reinforcing layerformed on the outer surface of the blade root portion by curing theresin, in the reinforcing method for the wind turbine blade according toan embodiment.

DETAILED DESCRIPTION

Several embodiments of the present invention will be described belowwith reference to the attached drawings. However, dimensions, materials,shapes, relative arrangements, and the like of components described inthe embodiments or depicted in the drawings are not intended to limitthe scope of the present invention thereto and are only illustrative.

For example, not only do expressions for relative or absolutearrangements such as “in a certain direction”, “along a certaindirection”, “parallel”, “orthogonal”, “central”, “concentric”, and“coaxial” exactly represent such arrangements but also representrelative displacements with tolerances or such angles or distances asallow the same functions to be fulfilled.

For example, not only do expressions for equal states of things such as“the same”, “equal”, and “homogeneous” represent exactly equal statesbut also represent states with tolerances or such differences as allowthe same functions to be fulfilled.

For example, not only expressions for shapes such as a rectangular shapeand a cylindrical shape represent shapes such as a rectangular shape anda cylindrical shape in a geometrically strict sense but also representsuch shapes including a recessed and protruding portion or a chamferedportion to the extent that the same effects are produced.

On the other hand, the expression “comprising a component”, “containinga component”, “being provided with a component”, “including acomponent”, or “having a component” is not an exclusive expression thatexcludes the existence of other components.

FIG. 1 is a schematic diagram depicting a wind turbine generator systemaccording to an embodiment. FIG. 2 is a perspective view depicting theentire wind turbine blade according to an embodiment. FIG. 3 is aperspective view depicting a reinforced portion (FRP reinforcing layer)of the wind turbine blade according to an embodiment.

As depicted in FIG. 1, the wind turbine generator system according to atleast several embodiments of the present invention (hereinafter referredto as a windmill 100) includes a rotor 101 including a plurality of (inthe example illustrated in FIG. 1, three) wind turbine blades 1 and ahub 102 to which the wind turbine blades 1 are attached, a nacelle 103rotatably supporting the rotor 101 via a main shaft and a main bearingnot depicted in the drawings, a tower 104 that supports the nacelle 103so as to enable the nacelle to turn in the horizontal direction, and abase 105 on which the tower 104 is installed. The number of the windturbine blades 1 may be more or less than three.

As depicted in FIG. 2, in several embodiments, the wind turbine blade 1includes a blade main body 2 extending from a blade root portion 3toward a blade tip portion 4 and an FRP reinforcing layer 20 formed tocover at least a part of an outer surface 3A of the blade root portion 3of the blade main body 2. The blade main body 2 will be described below,and then, the FRP reinforcing layer 20 will be described in detail.

The blade main body 2 includes the blade root portion 3 attached to thehub 102 of the windmill 100, the blade tip portion 4 positioned furthestfrom the hub 102, and an airfoil portion 5 extending in a blade lengthdirection between the blade root portion 3 and the blade tip portion 4.The blade main body 2 has a leading edge 6 and a trailing edge 7extending from the blade root portion 3 to the blade tip portion 4. Anexternal shape of the blade main body 2 is defined by a suction surface11 (negative pressure surface) and a pressure surface 13 (positivepressure surface) opposite to the suction surface 11.

The “blade length direction” as used herein refers to a direction alongwhich the blade root portion 3 and the blade tip portion 4 are connectedtogether. The “chord direction (blade chord direction)” as used hereinrefers to a direction along a line (chord) with which the leading edge 6and the trailing edge 7 of the blade main body 2 are connected together.The “blade root portion” as used herein refers to a cylindrical portionof the wind turbine blade 1 that is cross-sectionally shaped generallylike a circle and that corresponds to, for example, a range of 5 m withreference to an blade root-side end face of the blade main body 2 of thewind turbine blade 1 (typically a range of 1 to 3 m from the end face).

In several embodiments, the blade main body 2 includes a firsthalf-section 10 (suction-side half-section) forming the above-describedsuction surface 11 side (suction side) and a second half-section 12(pressure-side half-section) forming a pressure surface 13 side(pressure side), with a boundary between the first half-section 10 andthe second half-section 12 corresponding to a line with which theleading edge 6 and the trailing edge 7 are connected together, forexample, as depicted in FIG. 2 and FIG. 3. That is, in severalembodiments, the blade main body 2 may include the suction-sidehalf-section (first section 10) and the pressure-side half-section(second section 12) joined to the suction-side half-section. The firstsection 10 and the second section 12 may define the external shape ofthe blade main body 2 by being integrally joined together at endscorresponding to the leading edge 6 and the trailing edge 7,respectively. In several embodiments, inner surfaces of the firstsection 10 and the second section 12 that face each other may be coupledtogether in the blade length direction by at least one shear web notdepicted in the drawings.

In several embodiments, the blade main body 2 may have a bolt hole 15 inthe blade root portion 3 through which the wind turbine blade 1 isattached to the hub 102. That is, as depicted in FIG. 3, a plurality ofbolt holes 15, through which bolts (T bolts) is tightened, are formed inthe blade root portion 3 at regular intervals along the circumferentialdirection thereof so that the wind turbine blade 1 is attached to thehub 102 through the bolt holes 15. The bolt holes 15 are formed bydrilling at positions at a predetermined distance from a hub-side endface of the blade root portion 3 according to the length of bolts notdepicted in the drawings.

In several embodiments, an FRP reinforcing layer 20 may be providedfurther toward the blade tip side than the extension range of the boltholes 15 in the longitudinal direction (blade length direction) of thewind turbine blade 1. This inhibits the FRP reinforcing layer 20 fromclosing the bolt holes 15 through which the wind turbine blade 1 isattached to the hub 102. Therefore, the wind turbine blade 1 can bereinforced without hampering a function to attach the wind turbine blade1 to the hub 102 via the bolt holes 15 or an operation of performingsuch attachment.

Now, the FRP reinforcing layer 20 will be described.

In several embodiments, the FRP reinforcing layer 20 includes aplurality of laminated fiber layers 24 and a resin 26 with which theplurality of fiber layers 24 is impregnated (see FIG. 11F and FIG. 11G).

Each of the fiber layers 24 may be formed of, for example, what iscalled a unidirectional (UD) layer in which fibers of a compositematerial (FRP such as CFRP or GFRP) including carbon fiber or glassfiber are arranged in alignment in a single direction. In this case, inthe FRP reinforcing layer 20, the fiber layers 24 may be oriented suchthat a fiber direction in the UD layer extends along the blade lengthdirection.

The number of the laminated fiber layers 24 is not particularly limited.However, in several embodiments, for example the number of the laminatedfiber layers 24 may be 10 or more and 100 or less. In severalembodiments, the fiber layers 24 may be laminated so as to have athickness that enables reinforcement for a needed strength correspondingto the distribution of stress near the blade root portion 3 of the windturbine blade 1. This allows the wind turbine blade 1 to beappropriately reinforced in accordance with the distribution of stressnear the blade root portion 3 of the wind turbine blade 1.

FIG. 4 is a diagram depicting the reinforced portion of the wind turbineblade according to an embodiment and illustrating the shape of both endsof the FRP reinforcing layer and a configuration area of the FRPreinforcing layer in the circumferential direction of the blade rootportion.

As depicted in FIG. 3 and FIG. 4, in several embodiments, the FRPreinforcing layer 20 may be formed such that, for example, both ends ofthe plurality of laminated fiber layers 24 in the circumferentialdirection of the blade root portion 3 may be tapered in a cross sectionof the blade root portion 3. This allows the thickness of the blade rootportion 3 in the circumferential direction thereof to vary sufficientlygradually to enable the wind turbine blade 1 to be reinforced whilesuppressing possible stress concentration. In several embodiments, thetapered shapes of both ends of the FRP reinforcing layer 20 in thecircumferential direction of the blade root portion 3 may have the samegradient. In other embodiments, the tapered shapes of both ends of theFRP reinforcing layer 20 in the circumferential direction of the bladeroot portion 3 may have different gradients.

In several embodiments, the FRP reinforcing layer 20 is formed, in thecircumferential direction of the blade root portion 3, within an angularrange of θ₀−50 degrees≤θ≤θ₀+50 degrees when the angular position of thecenter of a circular arc defined in a cross section of the blade rootportion 3 by at least one of the first section 10 (suction-sidehalf-section) and the second section 12 (pressure-side half-section) isdenoted by θ₀, as depicted in FIG. 4, for example. This allowsappropriate reinforcement of a part of the blade root portion 3 on whicha heavy load is imposed in a flap direction by bending stress.

Now, with reference to FIG. 5, the load imposed on the wind turbineblade 1 in the flap direction will be described. FIG. 5 is a schematicdiagram taken along arrow V-V in FIG. 2 and illustrating the shape ofthe wind turbine blade.

As depicted in FIG. 5, the wind turbine blade 1 has the blade rootportion 3 shaped like a cylinder cross-sectionally shaped generally likea circle and an airfoil portion 5 extending from the blade root portion3 to the blade tip portion 4 and cross-sectionally shaped generally likea blade (see a dashed line in FIG. 5). In FIG. 5, the flap direction isa direction corresponding to a line which is orthogonal to a directionof the chord connecting the leading edge 6 and the trailing edge 7, andwith which the suction side and the pressure side of the blade main body2 are connected together. At the time of a strong wind, a heavy loadacts on both ends of the blade root portion 3 in the flap direction,that is, a suction-side end 32A and a pressure-side end 32B of the bladeroot portion 3. Thus, reinforcing the suction or pressure side of theblade root portion 3 of the wind turbine blade 1 allows a significantreinforcing effect to be exerted on the wind turbine blade 1 and, inparticular, is important for providing additional reinforcement forincreasing fatigue strength in the blade length direction correspondingto the longitudinal direction of the wind turbine blade 1.

FIG. 6 is a diagram depicting the reinforced portion of the wind turbineblade according to an embodiment and illustrating the shape of both endsof the reinforced portion in the longitudinal direction of the windturbine blade. FIG. 7 is a diagram depicting a configuration of the FRPreinforcing layer in an embodiment.

In several embodiments, the FRP reinforcing layer 20 is formed suchthat, in a cross section along a longitudinal direction of the blademain body 2, both ends of the plurality of laminated fiber layers 24 inthe longitudinal direction may be tapered, for example, as depicted inFIG. 3, FIG. 6, and FIG. 7. This allows the FRP reinforcing layer 20including the plurality of fiber layers 24 impregnated with the resin 26to cover at least a part of the outer surface 3A of the blade rootportion 3 of the blade main body 2 for reinforcement. The FRPreinforcing layer 20 is formed such that, in a cross section along thelongitudinal direction of the blade main body 2, both ends of theplurality of laminated fiber layers 24 in the longitudinal direction aretapered. Thus, the thickness of the blade root portion 3 of the windturbine blade 1 including the FRP reinforcing layer 20 is inhibited fromvarying sharply in the longitudinal direction of the wind turbine blade1. Therefore, the FRP reinforcing layer 20 allows the wind turbine bladeto be reinforced while appropriately suppressing possible stressconcentration resulting from a load imposed on the blade root portion 3of the wind turbine blade 1 in the flap direction.

As depicted in FIG. 3 and FIG. 6, the blade root portion 3 of the blademain body 2 has a hollow shell structure and has an area where thethickness of the blade main body 2 is varied according to the neededstrength. Thus, for example, as depicted in FIG. 6, the blade rootportion 3 can be appropriately reinforced by providing the FRPreinforcing layer 20 on the outer surface 3A of the area where thethickness of the blade main body 2 is varied.

In several embodiments, the first tapered shape (the inclination angleof a first inclined portion 28) of the blade tip-side end of both endsof the plurality of laminated fiber layers 24 may be gentler than thesecond tapered shape (the inclination angle of a second inclined portion29) of the blade root-side end of both ends of the plurality oflaminated fiber layers 24, for example, as depicted in FIG. 3, FIG. 6,and FIG. 7.

Specifically, as shown in FIG. 6 the FRP reinforcing layer 20 may beformed such that, when a distance D1 extends, along the blade lengthdirection, from the blade root portion 3-side end of the FRP reinforcinglayer 20 in the blade length direction, that is, the blade root portion3-side end of the lowermost layer in the FRP reinforcing layer 20, tothe blade root portion 3-side end of the uppermost layer of the fiberlayers 24 corresponding to the uppermost layer in the FRP reinforcinglayer 20, a distance D2 extends, along the blade length direction, fromthe blade tip portion 4-side end of the lowest layer in the FRPreinforcing layer 20 to the blade tip portion 4-side end of theuppermost layer of the fiber layers 24 corresponding to the uppermostlayer in the FRP reinforcing layer 20, and a height H extends from theouter surface 3A of the blade main body 2 to an upper surface of theuppermost layer in the FRP reinforcing layer 20, a relation inExpression (1) is met.

[Math. 1]

H/D2<H<D1   (1)

In the above-described configuration, both ends of the plurality oflaminated fiber layers 24 may be formed such that the first inclinedportion 28 of the blade tip portion-side end, which has a spareinstallation area, is sufficiently gentler than the second inclinedportion 29 of the blade root portion-side end. Therefore, the thicknessof the blade root portion 3 in the longitudinal direction may varysufficiently gradually. This allows the wind turbine blade 1 to bereinforced while suppressing possible stress concentration resultingfrom a load in the flap direction.

In several embodiments, the first inclined portion 28 of the blade tipportion-side end of both ends of the plurality of laminated fiber layers24 may have an inclined surface with a gradient of 5% or less withrespect to the longitudinal direction. In other words, the firstinclined portion 28 may be formed so as to meet a relation in Expression(2) using the above-described distance D2 and height H.

[Math. 2]

H/D2≤0.05   (2)

In above-described configuration, the inclined surface of the blade tipportion-side end of the fiber layers 24 may have a sufficiently gentlegradient of 5% or less with respect to the longitudinal direction of thewind turbine blade 1. This enables the thickness of the blade rootportion 3 in the blade length direction to vary sufficiently gradually,allowing the wind turbine blade 1 to be reinforced while suppressingpossible stress concentration resulting from a load in the flapdirection.

In several embodiments, the second inclined portion 29 of the blade rootportion 3-side end of both ends of the plurality of laminated fiberlayers 24 may have an inclined surface with a gradient of 10% or lesswith respect to the longitudinal direction. In other words, the secondinclined portion 29 may be formed so as to meet a relation in Expression(3) using the above-described distance D1 and height H.

[Math. 3]

H/D1≤0.1   (3)

In the above-described configuration, the second inclined portion 29 ofthe blade root portion 3-side end may also be formed such that thethickness of the blade root portion 3 in the blade length directionvaries sufficiently gradually, allowing the wind turbine blade 1 to bereinforced while suppressing possible stress concentration resultingfrom a load in the flap direction.

In several embodiments, the PRP reinforcing layer 20 may include anintermediate layer 22 formed of a multidirectional fiber layer betweenthe outer surface 3A of the blade root portion 3 and the plurality offiber layers 24 (see, for example, FIG. 11C and FIG. 11G). Themultidirectional fiber layer as used herein refers to a layer in whichfibers are entangled with one another in different directions. Thisconfiguration allows the fiber layers 24 to be more appropriately bondedto the outer surface 3A of the wind turbine blade 1.

In several embodiments, the intermediate layer 22 may be, for example, adouble bias mat (DBM) material. The double bias mat material is a matmaterial that is a combination of fibers arrayed in two differentdirections (for example, ±45°). In several embodiments, the intermediatelayer 22 may be, for example, a chopped strand mat. The chopped strandmat is a sheet (non-woven cloth) into which fiber pieces (having alength of, for example, 5 to 200 mm) resulting from chopping of twistedyarns (strands) are dispersed uniformly in a non-oriented manner andshaped using a binding agent (for example, a polyester binder). Thechopped strand mat can be suitably used as the intermediate layer 22because of its non-directional substrate strength and its excellentperformance in impregnation, deforming, and mold conformance. In thisconfiguration, the fiber layers 24 can be more appropriately bonded tothe outer surface 3A of the wind turbine blade 1 by using the doublebias mat or the chopped strand mat in which the fibers are entangledwith one another.

In several embodiments, a polyester resin or an epoxy resin may be usedas the resin 26. In this case, the FRP reinforcing layer 20 can beformed by impregnating the fiber layers 24 with a thermoplastic resinsuch as the polyester resin or the epoxy resin, which is then cured. Forexample, if the fiber layers 24 are impregnated with the polyesterresin, which is then cured, the curing results from self-heating,eliminating the need for an external heating operation to allow the FRPreinforcing layer 20 to be easily and inexpensively formed. If the fiberlayers 24 are impregnated with the epoxy resin, which is then cured, theFRP reinforcing layer 20 can be formed which is more excellently bondedto the outer surface 3A of the blade root portion 3.

If an outer circumferential side of the blade root portion 3 of the windturbine blade 1 is to be reinforced, the wind turbine blade 1 maytemporarily be removed from the hub 102 and placed on the ground, and aplurality of operators may perform a reinforcing operation on a largearea of the blade surface. Thus, this case allows reinforcingoperability to be improved compared to a case where reinforcement isexecuted on an inner circumferential side of the blade root portion 3 onwhich only fewer operators can perform operation due to spacelimitations.

Now, a reinforcing method for the wind turbine blade 1 according toseveral embodiments will be described with reference to FIG. 8 to FIG.10 and FIG. 11A to FIG. 11G FIG. 8 to FIG. 10 are flowchartsillustrating a reinforcing method for the wind turbine blade accordingto an embodiment. Each of FIG. 11A to FIG. 11G is a schematic diagramillustrating the reinforcing method for the wind turbine blade accordingto an embodiment.

As depicted in FIG. 8, in several embodiments, when the wind turbineblade 1 is reinforced, the fiber layers 24 may be laminated on the outersurface 3A of the blade root portion 3 of the wind turbine blade 1 so asto cover at least a part of the outer surface 3A (step S1), thelaminated fiber layers 24 may be impregnated with the resin 26, which isthen cured (step S2), and the FRP reinforcing layer 20 may be formed onthe outer surface 3A of the blade root portion 3 (step S3). In thelaminating step, the above-described UD layers may be laminated as thefiber layers 24 (see FIG. 11C). In the step of impregnating the fiberlayers 24 with the resin 26 and curing the resin 26, the curing ispreferably performed after the laminated fiber layers 24 are impregnatedwith the resin 26 (see FIG. 11F) such that the resin 26 sufficientlyinfiltrates among the fibers in the fiber layers 24. In the step offorming the FRP reinforcing layer 20, a processing treatment for surfacefinish may be executed on the surface of the FRP reinforcing layer 20(see FIG. 11G) formed on the outer surface 3A of the blade root portion3.

In the step of laminating the fiber layers 24, the fiber layers 24 maybe laminated such that, in a cross section of the wind turbine blade 1in the longitudinal direction thereof, both ends of the laminated fiberlayers 24 in the longitudinal direction have tapered shapes (firsttapered shape and second tapered shape). In this method, the FRPreinforcing layer 20 is configured such that, in a cross section of theblade main body 2 in the longitudinal direction thereof, both ends ofthe plurality of laminated fiber layers 24 in the longitudinal directionhave tapered shapes, inhibiting the thickness of the blade root portion3 of the wind turbine blade 1 including the FRP reinforcing layer 20from varying sharply in the longitudinal direction of the wind turbineblade 1. Therefore, the method allows the wind turbine blade 1 to bereinforced while appropriately suppressing possible stress concentrationresulting from a load imposed on the blade root portion 3 of the windturbine blade 1 in the flap direction.

In several embodiments, the fiber layers 24 may be laminated such thatthe first inclined portion 28 of the blade tip-side end of both ends ofthe laminated fiber layers 24 has a smaller inclination angle than thesecond inclined portion 29 of the blade root-side end of both ends ofthe laminated fiber layers 24. The method allows the first inclinedportion 28 of the blade tip-side end of both ends of the plurality oflaminated fiber layers 24, which has a spare installation area, to beformed sufficiently more gently than the second inclined portion 29 ofthe blade root-side end of both ends of the plurality of laminated fiberlayers 24. Therefore, the method enables the thickness of the blade rootportion 3 in the longitudinal direction to vary sufficiently gradually,allowing the wind turbine blade 1 to be reinforced while suitablysuppressing possible stress concentration resulting from a load in theflap direction.

As depicted in FIG. 9, in several embodiments, at least theconfiguration area 8 of the outer surface 3A of the blade root portion 3where the FRP reinforcing layer 20 is to be configured may be roughened(step S11), the intermediate layer 22 may be formed in the roughenedconfiguration area 8 of the outer surface 3A of the blade root portion 3(step S12), and the fiber layers 24 may be laminated on the intermediatelayer 22 (step S13). In the roughening step, for example, a gel coatlayer is removed from the outer surface 3A of the blade root portion 3by sanding or the like to expose the FRP layer (see FIG. 7) in the bladeroot portion 3 as depicted in FIG. 11A. In the step of forming theintermediate layer 22, the DBM including the multidirectional fiberlayer or the chopped strand mat as described above may be stuck to theroughened configuration area 8 (see FIG. 11B).

The method may involve, instead of laminating the fiber layers 24directly on the outer surface 3A of the blade root portion 3, rougheningat least the configuration area 8 of the outer surface 3A of the bladeroot portion 3 where the FRP reinforcing layer 20 is to be configured,forming the intermediate layer 22 in the roughened configuration area 8,and laminating the fiber layers 24 on the intermediate layer 22.Therefore, the fiber layers 24 can be more appropriately bonded to theouter surface 3A of the wind turbine blade 1 by, for example, using, asthe intermediate layer 22, a material that can be appropriately bondedto the outer surface 3A and the fiber layers 24 of the wind turbineblade 1. Consequently, the FRP reinforcing layer 20 can be formed moreintegrally with the wind turbine blade 1, allowing the wind turbineblade 1 to be more firmly reinforced.

In several embodiments, in the step of forming the FRP reinforcing layer20, the laminated fiber layers 24 may be covered with a bag 40 (stepS31), a space enclosed by the outer surface 3A of the blade root portion3 and the bag 40 may be decompressed (step S32), and the resin 26 may beinjected into the decompressed space to impregnate the fiber layers 24with the resin 26 (step S33) as depicted in FIG. 10. That is, the methodmay be, for example, a method of vacuum assisted resin transfer molding(VaRTM). The vacuum assisted resin transfer molding, for example, doesnot need to use a massive facility such as an autoclave in reinforcingthe wind turbine blade 1, facilitating integral molding for the blademain body 2 and the reinforced portion (FRP reinforcing layer 20). Thevacuum assisted resin transfer molding also provides an appropriate workenvironment due to less volatilization of an organic solvent. In thestep of covering the fiber layers 24 with the bag 40, for example, asdepicted in FIG. 11D, the fiber layers 24 are covered with the bag 40such that the fiber layers 24 are enclosed and the space between an endof the bag 40 and the outer surface 3A of the blade root portion 3 issealed in an airtight manner using a seal 46. In the decompressing step,air in the internal space enclosed by the bag 40 and the outer surface3A is sucked (ventilated) toward the outside of the bag 40 via a suctionport 44 provided in a part of the space, for example, as depicted inFIG. 11E. In the impregnating step, the resin 26 is injected into thedecompressed bag 40 through an injection port 42 provided at a positiondifferent from the position of the suction port 44, for example, asdepicted in FIG. 11F.

In the method, the fiber layers 24 laminated on the outer surface 3A ofthe blade root portion 3 are covered with the bag 40, the space enclosedby the outer surface 3A of the blade root portion 3 and the bag 40 isdecompressed, and the resin 26 is injected into the decompressed space.Therefore, the resin 26 can be infiltrated throughout the fiber layers24, providing an FRP reinforcing layer 20 having few voids and a highstrength.

The embodiments of the present invention have been described. However,the present invention is not limited to the above-described embodimentsand includes variations of the embodiments and appropriate combinationsof the variations.

1. A wind turbine blade comprising: a blade main body extending from ablade root portion toward a blade tip portion; and an FRP (FiberReinforced Plastic) reinforcing layer formed so as to cover at least apart of an outer surface of the blade root portion of the blade mainbody, wherein the FRP reinforcing layer includes: a plurality oflaminated fiber layers; and a resin with which the plurality of fiberlayers is impregnated, and the FRP reinforcing layer is formed suchthat, in a cross section along a longitudinal direction of the blademain body and over the entire region of the FRP reinforcing layer in thelongitudinal direction, a bottom surface of the plurality of laminatedfiber layers extends linearly in the longitudinal direction along theouter surface of the blade root portion and both ends of the pluralityof laminated fiber layers in the longitudinal direction thereof aretapered.
 2. A wind turbine blade comprising: a blade main body extendingfrom a blade root portion toward a blade tip portion; and an FRP (FiberReinforced Plastic) reinforcing layer formed so as to cover at least apart of an outer surface of the blade root portion of the blade mainbody, wherein the FRP reinforcing layer includes: a plurality oflaminated fiber layers; and a resin with which the plurality of fiberlayers is impregnated, and the FRP reinforcing layer is formed suchthat, in a cross section along a longitudinal direction of the blademain body, a bottom surface of the plurality of laminated fiber layersextends linearly in the longitudinal direction along the outer surfaceof the blade root portion and both ends of the plurality of laminatedfiber layers in the longitudinal direction thereof are tapered, andwherein each end of the FRP reinforcing layer in the longitudinaldirection is tapered to incline inwardly in a radial direction of theblade root portion toward an outer edge of the FRP reinforcing layer inthe longitudinal direction.
 3. The wind turbine blade according to claim1, wherein a first tapered shape of a blade tip-side end of both of theends of the plurality of laminated fiber layers is different from asecond tapered shape of a blade root-side end of both the ends of theplurality of laminated fiber layers.
 4. The wind turbine blade accordingto claim 1, wherein the first tapered shape of the blade tip-side end ofboth of the ends of the plurality of laminated fiber layers has aninclined surface with a gradient of 5% or less with respect to thelongitudinal direction.
 5. The wind turbine blade according to claim 1,wherein the FRP reinforcing layer includes an intermediate layer betweenthe outer surface of the blade root portion and the plurality of fiberlayers and comprising a multidirectional fiber layer.
 6. The windturbine blade according to claim 5, wherein the intermediate layer is aDBM (Dense Bituminous Macadam) or a chopped strand mat.
 7. The windturbine blade according to claim 1, wherein a number of laminated fiberlayers in the plurality of laminated fiber layers is 10 or more and 100or less.
 8. The wind turbine blade according to claim 1, wherein theresin is a polyester resin or an epoxy resin.
 9. The wind turbine bladeaccording to claim 1, wherein the blade main body includes: asuction-side half-section; a pressure-side half-section joined to thesuction-side half-section, and the FRP reinforcing layer, in thecircumferential direction of the blade root portion, has an angularrange of θ₀−50 degrees≤θ≤θ₀+50 degrees when an angular position of acenter of a circular arc defined in a cross section of the blade rootportion by at least one of the suction-side half-section or thepressure-side half-section is denoted by θ₀.
 10. The wind turbine bladeaccording to claim 1, wherein the blade main body has in the blade rootportion a bolt hole through which the wind turbine blade is attachableto a hub, and the FRP reinforcing layer is provided farther toward ablade tip side than an extension range of the bolt hole in thelongitudinal direction.
 11. The wind turbine blade according to claim 2,wherein a taper angle of a first tapered shape of a blade tip-side endof both the ends of the plurality of laminated fiber layers is less thana taper angle of a second tapered shape of a blade root-side end of boththe ends of the plurality of laminated fiber layers.
 12. The windturbine blade according to claim 2, wherein the first tapered shape ofthe blade tip-side end of both the ends of the plurality of laminatedfiber layers has an inclined surface with a gradient of 5% or less withrespect to the longitudinal direction.
 13. The wind turbine bladeaccording to claim 2, wherein the FRP reinforcing layer includes anintermediate layer positioned between the outer surface of the bladeroot portion and the plurality of fiber layers and formed of amultidirectional fiber layer.
 14. The wind turbine blade according toclaim 13, wherein the intermediate layer is a DBM or a chopped strandmat.
 15. The wind turbine blade according to claim 2, wherein the numberof the laminated fiber layers is 10 or more and 100 or less.
 16. Thewind turbine blade according to claim 2, wherein the resin is apolyester resin or an epoxy resin.
 17. The wind turbine blade accordingto claim 2, wherein the blade main body includes: a suction-sidehalf-section and a pressure-side half-section that is joined to thesuction-side half-section, and the FRP reinforcing layer is formed, inthe circumferential direction of the blade root portion, within anangular range of θ₀−50 degrees≤θ≤θ₀+50 degrees when an angular positionof a center of a circular arc defined in a cross section of the bladeroot portion by at least one of the suction-side half-section or thepressure-side half-section is denoted by θ₀.
 18. The wind turbine bladeaccording to claim 2, wherein the blade main body has in the blade rootportion a bolt hole through which the wind turbine blade is attached toa hub, and the FRP reinforcing layer is provided further toward a bladetip side than an extension range of the bolt hole in the longitudinaldirection.